The exhaust gas of diesel engines, gasoline engines, and other internal combustion engines includes, for example, carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NOX), particulate matter (PM), and other constituents. The internal combustion engines are mounted with exhaust purification systems for removing these constituents.
Japanese Patent Publication (A) No. 2007-154794 discloses an exhaust purification system of an internal combustion engine which is provided with a plurality of branch passages, exhaust purification catalysts which are arranged in the branch passages, and fuel addition valves which are arranged at the upstream sides of the exhaust purification catalysts. This exhaust purification system is provided with heater-equipped catalysts at the upstream sides of the exhaust purification catalysts of part of the branch passages among the plurality of branch passages and reduces the flow rates of exhaust of the branch passages which are provided with the heater-equipped catalysts when warming up the exhaust purification catalysts. Further, this discloses to concentratedly run the exhaust through the other branch passages to warm the exhaust purification catalysts at the other branch passages. For the branch passages reduced in exhaust flow rates, the heater-equipped catalysts are electrified to warm up the exhaust purification catalysts. Further, this publication discloses to stop the electrification and inject fuel from fuel addition valves when the heater-equipped catalysts reach the activation temperature so as to raise the temperature of the exhaust by the oxidation reaction of the fuel occurring at the heater-equipped catalysts.